It is well known that the accumulation of ice on aircraft surfaces, particularly the leading edges of wings and engine inlet surfaces, is a dangerous condition. A layer of ice on the order of as little as a few centimeters in thickness on the leading edges of aircraft wings, for instance, has been shown to result in flow separation and consequential interruption of lift, possibly even resulting in the crash of the aircraft. At the very least, the additional drag on the aircraft caused by ice results in increased use of fuel and unstabilized flight.
As a result, substantial efforts have been made to prevent the formation of ice on, and/or to remove ice from, such aircraft surfaces. One of the most common methods presently used for ice prevention/removal from leading edge surfaces is heating, by means of bypass techniques using excess heat from the aircraft engines. Although bypass systems are reasonably effective, they do have some disadvantages. A bypass system requires a separate structure to route the heated air, which adds additional weight to the aircraft. The air from the engines must first be cooled and the system for doing this is rather complex. Further, bypass de-icing with heated air increases fuel use and thus increases cost on this basis as well. In addition, the use of bypass techniques will likely become undesirable as newer engines are developed which produce less excess heat and have lower core temperatures. Stability problems may result if additional heat is drawn from the engines for bypass, due to further reduction in core temperatures.
As an alternative to the engine bypass heating system, an electromagnetic impulse system was developed to mechanically force the ice from aircraft surfaces. In such a system generally, a bank of high voltage capacitors is discharged through a coil which is positioned adjacent the interior of a leading edge surface of the aircraft, such as a wing, resulting in a rapidly forming and collapsing magnetic field which induces eddy currents into the thin metal skin of the aircraft. The magnetic field creates a repulsive force which is quite large but has a very short duration. This results in a rapid acceleration of the metal skin of the aircraft, although the actual movement of the skin is small, which acts to debond and in essence "shatter" the ice from the aircraft surface.
An early disclosure of such a system is found in British Patent Specification No. 505,433, dated May 5, 1939, to Goldschmidt. To the best of applicant's knowledge, such a system has never been implemented. U. S. Pat. No. 3,549,964 to Levin et al, dated 22 December 1970, is a later example of continuing work in this area, referred to generally as electro-impulse de-icing or EIDI. Additional research into EIDI techniques has been done at Wichita State University in Wichita, Kansas, as well as by individual aircraft companies. However, all such systems are characterized by the use of relatively high voltage, i.e. at least 800V-2000V and correspondingly large (and complex) power supplies. In combination with the necessary cables, such a system is relatively heavy. Typically, only a very few power supplies are used, such as one or two for each wing, in combination with a plurality of individual coil units positioned at selected locations along the interior surface of the wing. The coil units are arranged in parallel, and each coil unit has its own control switch. The power supplies are typically positioned in the main fuselage portion of the aircraft, with long cables connecting the power supplies to the coil units.
Such an approach has significant disadvantages. First, the use of high voltage has inherent risks, including the risk of fire/explosion due to arcing in those areas where fuel could be present. In addition, such a system is relatively bulky and heavy, and requires the use of transformers or other inductive devices, as well as timing circuits and multiplexing circuits. The failure of any one of the cables or switches in the system will disable the associated power supply and hence at least a significant part of the EIDI system. Still further, such a system is also typically quite expensive.
As a result, even though EIDI technology has been shown generally to have substantial technical merit, it has not been widely used commercially.